This invention relates generally to illumination systems, and more particularly to multi-color (red, green and blue, for example) light-emitting-diode driver circuitry that provides improved system efficiency and thermal performance, with reduced cost.
A light-emitting diode is a type of semiconductor device, specifically a p-n junction, which emits electromagnetic radiation upon the introduction of current thereto. Typically, a light-emitting diode comprises a semiconducting material that is a suitably chosen compound, for example a gallium-arsenic-phosphorus compound. By varying the ratio of phosphorus to arsenic, the wavelength of the light emitted by a light-emitting diode can be adjusted, thereby providing light of different colors. By using different semiconductor materials (for example, AlinGaP and InGeN) and controlled xe2x80x9cimpuritiesxe2x80x9d, different color LED (such as red, green and blue) can be made.
With the advancement of semiconductor materials and optics technology, light-emitting diodes are increasingly being used for illumination purposes. For instance, high brightness light-emitting diodes are currently being used in automotive signals, traffics lights and signs, large area displays, etc.
Currently, electronic driver circuits that drive mono-color light-emitting-diode arrays typically employ a flyback converter. A flyback converter is used to drive an light-emitting-diode array lamp by converting an input line voltage (such as a 230 Vac input line) into a voltage source (such as a 30V voltage source). A linear regulator is then used to regulate the light-emitting-diode array current.
For systems that employ multiple color light-emitting-diode arrays, the electronic driver circuits that are currently used typically employ multiple power converters. For example, FIG. 1 illustrates a typical scheme for a driver circuit in which the light-emitting-diode arrays have three colors. Specifically, FIG. 1 shows system 10 having light-emitting-diode arrays that are red, blue and green, wherein each light-emitting-diode array employs a separate power converter.
For instance, red light-emitting-diode array 12 employs power converter 22, while green light-emitting-diode array 14 employs power converter 24 and blue light-emitting-diode array 16 employs power converter 26. The intensity of the light from each of the light-emitting-diode arrays is measured by photodetector 18, which transmits a signal corresponding to the intensity to control block 30. Control block 30 is configured to alternately turn the respective light-emitting-diode arrays on and off, so that the intensity of each may be measured independently. In addition, control block 30 transmits signals to power converters 22, 24 and 26, each of which employs the signal to control a flow of current through their respective light-emitting diode.
However, the redundancy of components for separate power converters for each light-emitting-diode array increases the size and cost of the driver circuit and reduces the efficiency of the circuit. Therefore, there exists a need for an improved light-emitting diode driver circuit that does not suffer from the problems of the prior art, as discussed above.
In accordance with one embodiment, the present invention relates to a white light LED driver circuit with multiple local feedback output current control circuits. The driver circuit comprises a power supply source and a transformer having a primary winding coupled to, and configured to receive current from, the power supply. The transformer also has a plurality of secondary windings coupled to the primary winding. The circuit also comprises a plurality of light-emitting-diode arrays, wherein each light-emitting-diode array is coupled to one of the secondary windings, in a local feedback control arrangement.
A main controller is coupled to a first of the light-emitting-diode arrays and is configured to control a flow of current to the primary transformer winding. The circuit also comprises a plurality of secondary controllers. Each of the secondary controllers is coupled to a corresponding light-emitting-diode array. In addition, each of the secondary controllers are configured to control a flow of current to its corresponding light-emitting-diode array.
According to one embodiment of the invention, each of the light-emitting diodes has a resistor coupled to its cathode terminal. An output signal of each resistor is transmitted to the respective controller and is employed to determine the appropriate current flow to the light-emitting-diode array. The driver circuit may be configured as either a flyback converter, wherein the primary transformer winding is wound in the opposite direction of the secondary transformer windings, or as a forward converter, wherein the primary transformer winding is wound in the same direction as secondary transformer windings.